1. Field of the Invention
The present invention relates to a thin film phosphor and, more particularly, a thin film phosphor fabricated by forming a raw material of the phosphor on a surface of a workpiece material such as a substrate, a phosphor product manufactured using the same, and a method for fabrication thereof.
2. Description of the Related Art
Flat panel displays (FPDs) currently developed as an information transmission device are generally classified into light receiving types such as liquid crystal display (LCD) and light emitting types such as plasma display panel (PDP), field emission display (FED), electroluminescence display (ELD), vacuum fluorescent display (VFD), etc. Although the light emitting type FPD is distinguishable into different type devices in terms of structure and light emission source, all of these devices commonly make use of a phosphor. Such phosphor may be divided into a powder phosphor and a thin film phosphor.
A result of comparing characteristics between the thin film phosphor and the powder phosphor is shown in the following table. As shown in the table, the thin film phosphor exhibits superior characteristics over the powder phosphor except for light emission efficiency and, especially, has remarkably excellent resolution.
TABLE 1Comparison of characteristics betweenthin film phosphor and powder phosphorFeatureThin film phosphorPowder phosphorLight emissionInferiorSuperiorefficiencyCrystal structureSingle crystalpolycrystallineDecay time ( 1/1010 ms12 msoriginal luminance)ResolutionLess than 1 μm5 to 10 μmScreen shadeSuperiorInferiorLifespanSuperiorInferiorThermal, mechanicalSuperiorInferiorstabilityProduction costHighLow
Among factors effecting light emission efficiency of a thin film phosphor, there are a quantitative ratio of elements in the thin film, optimization of additives, crystallinity, surface conditions of the thin film, growth orientation, etc. A principal cause of lowering effects of the thin film phosphor is light loss due to total internal reflection of 80 to 90% light. For a powder phosphor, since light is emitted outside after internal reflection several times, the total internal reflection causes only a small reduction in light emission efficiency. However, for a thin film phosphor with a flat thin film, due to total internal reflection, only light incident on a surface of the film, wherein the light has an incident angle less than a critical angle, is emitted outside. Briefly, only several % of light from the phosphor is emitted outside.
Although the powder phosphor has excellent light emission efficiency, a display resolution is restricted due to a size of particle, poor reliability and processing difficulties are entailed in patterning, etc. Therefore, a thin film phosphor is generally used in related arts.
A thin film phosphor is generally fabricated by conventional methods such as sputtering, pulsed laser deposition (PLD), e-beam, sol-gel, chemical vapor deposition (CVD), and so forth. However, as disclosed above, such a thin film phosphor fabricated by the foregoing methods entails problems of considerably decreased such as light emission efficiency, compared to a powder phosphor. In order to solve the problems, a variety of processes including, for example, rough processing of a surface of the thin film in order to decrease total internal reflection, or other treatments to improve crystallinity and/orientation have been proposed.
Recently, in order to improve light emission efficiency of the thin film phosphor, heat treatment at a high temperature is well known. According to such treatment, when the thin film is heated at a high temperature of more than 1,000° C. after forming the same, the phosphor has crystallinity substantially equal to powder and a rough surface thereof, thus a high light is emission efficiency can be expected. However, since a FPD uses a glass substrate which cannot be heated at a temperature of more than 600 to 700° C., the thin film phosphor encounters a problem of not being applied to a practical process for manufacturing of FPDs.
Conventional methods for formation of thin film phosphors do not meet a recent tendency to increase in scale of a substrate, a thin film phosphor fabricated by the conventional method has poor luminance, and transparency of the phosphor is not suitably obtained due to interference patterns at a boundary between the phosphor and a substrate and/or light reflection. Accordingly, use of the thin film phosphor is considerably restricted.